1. Field of the Invention
This invention relates to methods and apparatus for suspending worker's scaffolds over the sides of buildings, towers, and the like for purposes of painting, window washing, maintenance, inspection or the like, particularly to such methods and apparatus that employ davits from which such scaffolds are to be suspended, and to methods and apparatus for securing the safety of such davits and of worker's scaffolds suspended therefrom, without compromising the integrity of a flat roof surface or a corresponding deck or the like in connection with which the davits are installed.
2. Background Information
For purposes of painting, window washing, maintenance, inspection or the like, it has been the practice to provide pairs of davits on the roofs of buildings, and from such davits there is suspended a scaffold that can be raised and lowered along the side of the building on which workers may stand to carry out their tasks. These davits are not permanent fixtures on a building; instead, socket pedestals are customarily provided around the periphery of the roof top, so that portable davit sockets can then be moved into such pedestals as the work may require, the davits then being placed into those davit sockets.
This general procedure is illustrated in FIG. 1 (prior art), which shows in schematic form a cross-section of one end of a building, including the roof top and parapet. Inboard from the parapet is a socket pedestal into which has been placed a davit socket (also shown separately to illustrate the wheels thereon), and one davit is shown inserted into the davit socket so as to extend beyond the building edge and permit suspension of a scaffold from a cable hanging down the side of the building. A safety line is also shown and exemplifies the need for the present invention.
Such safety lines are generally required, as set forth, e.g., in Title 8, General Industry Safety Orders, of the California OSHA regulations, p. 573, to ensure that in the event of disconnection of a scaffold from a davit, a second connection is made (or is accessible) between the scaffold and a structural location on the building. However, although the aforesaid disposition of structures in accordance with those regulations serves to provide for the safety of workers located on the scaffolding down along the side of the building, those same structures introduce substantial safety hazards to persons working on the roof top. Even in the absence of an installed davit socket and davit, for example, the socket pedestals will themselves present an obstacle extending perhaps a foot or so inwardly on the roof top from the parapet so as to create a hazard of tripping.
Such pedestals also act as an attractive nuisance, in that they are typically formed of one-inch steel plate, capable of bearing the weight of a person, and thus they create the temptation for persons to climb up and stand on them so as to come into danger of falling over the parapet. Again even in the absence of a davit socket and davit, some six feet or so inwardly from the socket pedestal there is associated therewith a safety anchor, which extends above the roof line to produce another tripping hazard. The safety anchor also introduces a substantial structural disadvantage in that a roof top that could otherwise be formed as a single, unbroken and leak-proof surface must have apertures formed therein so as to accommodate the safety anchors. It is difficult to maintain water-tight integrity between such upwardly extending structures and a flat roof top, hence the need for such a safety anchor introduces additional maintenance expenses. When the davit is installed it is necessary to use the safety line that connects back to the safety anchor, since the parapet itself is generally not a structural but only an add-on feature of the roof. The safety line then introduces additional hazard, not only for tripping, but a person walking near the periphery of the roof might well be "clothes-lined" by the safety line, by which is meant that when so walking in the dark a body could collide with the safety line.
Illustrative of the prior art in this field is U.S. Pat. No. 4,714,226 issued Dec. 22, 1987 to Tracy, which describes a "base member" (comparable to the socket pedestal noted above) mounted within the non-structural roof surface adjacent the roof parapet, a portable davit socket that can be wheeled into that base member and be removably mounted therein, and a davit that can be removably mounted into the davit socket. A particular feature of this device is that the davit socket incorporates a swivel, so that the socket can be rotated into a slanted position for easy insertion of the lower end of the davit, and then be rotated back to the vertical so as to hold the davit vertically.
U.S. Pat. No. 4,538,705 issued Sep. 3, 1985 to Leivestad addresses a different aspect of operating a davit-and-scaffold system, namely, the matter of moving the scaffold from an initial position atop the roof to its position when in use, i.e., suspended down the side of the building wall. For such purpose, the davit is made to be of a height such that the scaffold can be suspended therefrom at a position that is higher than the parapet, whereupon a stanchion apparatus permits the workers who have entered onto the scaffold to rotate the davits from which they are suspended outwardly from the building, until the scaffold is indeed positioned outwardly from the parapet and can be lowered as needed.
Another aspect of operating a davit-and-scaffold system lies in providing movement of the scaffold horizontally, along the building wall. This issue is addressed in U.S. Pat. No. 4,811,819 issued Mar. 14, 1989 to Sugiyama, wherein is described a set of mounting frames that are fixedly mounted to the roof parapet and to which is then attached a rail apparatus that permits horizontal as well as vertical motion of a scaffold (or "gondola") suspended therefrom. The use of such a device depends upon the parapet being structural in nature, i.e., it must be an integral part of the building structure and of a strength such that davits attached thereto need not have tiebacks or other such additional safety features added thereon. U.S. Pat. No. 5,343,979 issued Sep. 6, 1994 to Goto describes a similar device, likewise mounted to a structural parapet, that further includes a winch system for providing powered movement of the gondola.
As a means for mounting into some permanent building structure some vertical member, it is known for example to provide in the structure of a staircase an integral mount into which may be placed the "posts" of a stair rail. Such a device is described in U.S. Pat. No. 4,598,524 issued Jul. 8, 1986 to Cheng, wherein a U-shaped metal frame is nailed to a wooden form board around which is to be poured the structural concrete, so that when the concrete is set and the form board is removed, the aforesaid frame will have become integrated into the concrete base of the stairway, and the stair rail posts may be inserted therein. Such a procedure is not applicable to the removable mounting to a roof top of davits for the suspension of a workers' scaffold, however, since such a simple concrete structure is not adapted to withstand any substantial torque or moment of force (e.g., as would be caused by pulling the top of a stair rail in the Cheng device sideways) as is produced in a davit-and-scaffold system by the weight of the scaffold (and workers) pulling downward on the topmost and outward end of the davit.
What is needed and would be useful, therefore, is a method and apparatus for providing in the most common buildings that lack structural parapets the essential safety features with regard to persons working on a scaffold extending down the side of a building, without at the same time creating substantial hazards for persons working on the roof top of that building. It would also be of substantial value to provide such safety features without compromising the water-tight integrity of the roof top. The present invention serves both such purposes, as will now be described.